The invention pertains to an improved method of producing scrambled images which can be used in a method for improving the security of printed matter. Many printed documents can have significant financial value, such as securities, government checks, lottery tickets or game cards. Of course, the temptation always exists to reproduce or counterfeit such documents for financial gain. Especially in the case of high volume items with uncontrolled distribution, such as lottery tickets, where ownership is impossible to track, an inexpensive and flexible method is necessary to inhibit and in detection of such unauthorized replication.
Numerous methods exist to try to accomplish the above goals of various sophistication and expense. These can range from the choice of special materials to complicated printed patterns, to codes hidden under removable material, and to relatively expensive devices, such as holographs, incorporated into the printed matter.
The present invention specifically relates to the use of multiple interlineated images to form scrambled images which cannot be perceived unless viewed through an appropriate lineated lens, such as a lenticular lens or a grating screen. That is, two or more images are superimposed on each other by having alternating linear parallel spaces in which each image is represented such that if a set of alternating linear parallel spaces is viewed by itself (for two superimposed images), one of the images would be clear. Of course, the finer the lineation, the clearer the image will be to the eye. A method of the present invention is an improved process of linear approximation of each image, and then interlineating the two sets of lines to form the scrambled image.
The general concept of forming such interlineated multiple images is well known, and is familiar in use in conjunction with lenticular lenses in novelty items which change images when the angle of observation is changed and in forms of stereoscopic images viewed simultaneously by the viewer's two eyes.
Prior art patents in the general field of interlineated images include the following:
U.S. Pat. No. 2,815,310 (Anderson) discloses a process of making changeable picture displays. The method described includes use of a lineated grating screen placed in front of the film plate of a camera as one image is photographed, and then moving the plate with respect to the grating prior to exposing the second image. The disadvantage of this method is that a complicated camera device is used in exposing the original images, which is both expensive and an inconvenient way to create the interlineated image.
U.S. Pat. No. 3,178,993 (Ferris, et al.) discloses a cryptographic device using a lenticular screen, but which is not composed of parallel linear elements and is, therefore, not capable of combining multiple images for separate viewing.
U.S. Pat. Nos. 3,524,395; 3,937,565 and 4,092,654 (all to Alasia) describe various photographic methods for creating screened images which also require complicated machinery to move the object film with respect to the images being exposed.